1. Field of the Invention
The present invention relates to a high chromium heat resistant cast steel material applicable to a thermal power generation steam plant etc. and to a pressure vessel, such as a steam turbine casing, formed thereof.
2. Description of the Prior Art
As a heat resistant material applied to a thermal power generation steam plant in the prior art, there have been used CrMo cast steel, 2.25% CrMo cast steel, CrMoV cast steel, 12 Cr cast steel, etc.
In the heat resistant material applied to the thermal power generation plant in the prior art, use of a cast steel material of a low alloy steel, such as CrMo cast steel, 2.25% CrMo cast steel, CrMoV cast steel and the like, has been limited to a plant of steam temperature of up to 566.degree. C. for reason of limitation of a high temperature strength.
On the other hand, 12 Cr cast steel material (as disclosed by the Japanese laid-open patent application Sho 59-216322, for example), which is superior in the high temperature strength to the cast steel made of the low alloy steel, can be applied to a plant of steam temperature of nearly up to 600.degree. C., but being short of a higher temperature strength, it is hardly applied as a pressure vessel of a steam turbine casing and the like.